Surface geometry based hydrophobicity of the PDMS for microfluidic devices

In this report, the surface hydrophobicity of PDMS was investigated using two methods of preparations. The first method was performed by changing the surface roughness through the use of different molds. The second method was performed by varying the reconstitution ratio (volume of elastomer base to volume of elastomer curing) of the PDMS. Variation in the hydrophobicity of the PDMS was characterized by measuring the contact angle of a liquid droplet against the surface of the PDMS. The results showed that both the surface roughness and the reconstitution ratio of the PDMS positively correlated with the contact angle measured regardless of the liquid used. The maximum and minimum contact angle obtained were θ_r = (138 ± 3)° and θ_r = (99 ± 3)°, respectively. The results demonstrate a straightforward way of fabricating microfluidic devices using PDMS with controlled hydrophobicity. (paper)